Possible new A77 camera problem? need help..

Hello,new to posting on forms but a long time reader...I upgraded from a 300 to new a77 v.1.07 from amazon deal two weeks ago.Bought the body only as I have a few Minolta lenses and kit from a 300....lots to learn here for sure bought garys e book. My question is ; sometimes when I review taken photos with the playback button and the multi selector to go back,I hear the shutter fire off.....this has happened afew times.Ive checked no picture has been taken.Ihave a concern here as is the camera defective or is it the nature of the beast. No other concerns .Thanks for any insights.